1. Field of the Invention
This invention is concerned with a process and apparatus for heating a particulate material by directly contacting with heat transfer media within a continuously rotating cylindrical drum.
2. Description of the Prior Art
It is known in the art to effect heat exchange between piece-shaped materials and heated or cooled loose balls by directly contacting the material being treated with the heat carrying balls in a rotary heat exchanger which is rotated around a substantially horizontal axis. In the rotary heat exchanger, the material is introduced into the drum from one end of the drum and the heat carrying balls are introduced into the other end of the drum. During the rotation of the drum, the material and the heat carrying balls are brought into direct contact with each other in the drum and the material flows in one direction through the drum and the heat carrying balls flow in the opposite direction through the drum.
The rotary heat exchanger known in the art is generally not capable of effectively causing the countercurrent flow of the material and the heat carrying balls in th drum. The reason for this is that the heat exchanger is rotated around the horizontal axis and that the material in such a rotary device is agitated in a relatively resting position. Furthermore, this type of apparatus exposes only a small heat exchanger area of the material with the result that direct heat transfer between the heat carrying balls and the material as a whole is not efficient. It may be possible to incline the heat exchanger at an angle so as to effect the countercurrent flow of the material and the heat carrying balls satisfactorily in the drum. In this instance, the heat exchanger must be rotated at a relatively high speed for causing the heat carrying balls to flow from the low end to the high end of the drum which results in contamination or segregation of the material due to abrasion of the heat carrying balls during the rotation of the drum.